Metrology and Simulation with Progressive Addition Lenses

Abstract

The condition in which the eye loses the ability to focus on near objects is called presbyopia. The use of Progressive Addition Lenses (PALs) is one alternative to treat this condition. PALs have a continuous change in power from the top of the lens to the bottom to avoid abrupt change in power. The increment of power in progressive addition lenses is accomplished by increasing the lens curvature from the upper part of the lens to the lower part of it. PALs consist of one freeform surface that provides this power change and the other surface is typically spherical (or aspheric) with its shape chosen to meet the wearer’s distance prescription. Because of its application, progressive lenses should be prescribed, made and tested in a very short period of time. A variety of testing methods have been developed through the years. However, these tests are designed to test symmetric optical elements, or use additional optics that are very expensive. What is needed is a new technique that can overcome these difficulties in an economic and fast way. In this dissertation, several methods were implemented to test the freeform surface shape of a Progressive Addition Lens. Two different types of methods were used: contact methods such as the use of a linear profilometer, and a Coordinate Measurement Technique (CMM); non-contact methods such as the SCOTS Test by refraction, and ultraviolet (UV) deflectometry. Besides surface shape, acceptance of progressive addition lenses must be studied. A methodology to characterize the visual performance of Progressive Addition Lenses is presented with scene simulation of how the wearer sees through the spectacle. Simulated images are obtained by calculating the point spread function through a lens-eye model in function of gaze angle. A modified superposition technique which interpolates the psfs for different gaze angles, as well as at different object distances is developed and used to create simulated images. Such scene simulations would allow patients to examine the variety of tradeoffs with the various treatment modalities and make a suitable choice for treatment.